The future of Hawaii's Kilauea volcano is written in the Big Island's past

Looming above Kilauea's glowing lava rivers and explosions of ash, is the most massive mountain on Earth. Measured from its deep ocean base, the Mauna Loa volcano is taller than Mount Everest. It takes up over half of the Big Island.

And it's an omen of what's to come for Kilauea.

Hawaii's currently erupting and youngest volcano, Kilauea, peers up at Mauna Loa from some 9,000 feet below. Its latest bursts of lava, which started in early May and have since rumbled through neighborhoods, remind us that Kilauea is next in line to become a dominant presence on the Big Island, like Mauna Loa.

In the next 1,000 years or so, lava will almost certainly flow over nearly every inch of road and in every neighborhood on the volcano, as it continues growing. There's good precedent for this. Today, 90 percent of the volcano, located on the southeastern corner of the Big Island, is covered in lava that's less than 1,000 years old.

Mauna Loa, though far more ancient, once behaved in much the same way. The volcano emerged from the ocean some 300,000 years ago, and the U.S. Geological Survey (USGS) believes it has "grown rapidly upward since then."

"There's no reason to expect the events of Kilauea will be very much different than those that took place at Mauna Loa," Stanley Mertzman, a geoscientist at Franklin and Marshall College, said in an interview.

Kilauea sits to the right and below of Mauna Loa. Historic lava flows from both volcanoes are shown in light grey.

Image: National Park Service

"The only difference is there was no audience," said Mertzman of Mauna Loa, who has hiked to the snow-covered summit the volcano with his geology students.

Since 1983 alone, Kilauea has added around 570 acres of new land to the Big Island, and geologists expect the volcano to continue adding layer upon layer, building out and up like Mauna Loa, which is Hawaiian for "Long Mountain."

"If you look at Kilauea today and look back at the rather imposing Mauna Loa structure — that, simply, is what Kilauea will look like," said Mertzman.

Snow-covered Mauna Loa looms over the Hawaiian countryside.

Image: Getty Images/Lonely Planet Images

It will be quite similar in shape (Hawaiian volcanoes mature into gentle-sloping profiles) and quite big, but it's less certain if it will ever meet Mauna Loa's extraordinary height and girth.

The source of magma (underground lava) for Hawaiian volcanoes is a stationary "hot spot," a place underneath Earth's crust where rocks melt and then regularly ooze out, flowing up to the surface through subterranean channels. But exactly how that single hot spot ultimately feeds the Big Island's five volcanoes varies.

Of these five volcanoes, four will erupt again, said Jess Phoenix, a geologist that has sampled, hiked over, and studied the Big Island's volcanoes.

"That's a lot of demand on the hot spot," Phoenix, who is running for Congress in California, said. "So it would be interesting to see how Kilauea reacts."

An artist's conception of the Pacific tectonic plate traveling over the hot spot.

Image: usgs

Mauna Loa isn't the only giant presence on the Big Island. Its snow-capped neighbor, Mauna Kea, while not taking up as much mass or girth as Mauna Loa, is around 800 feet taller. Kilauea could become the third huge Big Island mountain.

"It's very possible that it could become the triplet," said Phoenix.

But, she noted that Mauna Loa is truly exceptional. It would be hard to top.

"It's extraordinary how big it is," she said. "It's the largest mountain on the planet."

Kilauea, though, is keeping up a good pace. In 1955, the volcano poured lava over 4,000 acres of the island, said Phoenix. And as the last few weeks specifically have shown, the activity hasn't relented.

Kilauea spraying lava out of the ground in 1955.

Image: usgs

"It's pretty active and there's no reason to see why that would change," said Phoenix, noting that molten rock will be brewing beneath its surface for hundreds of thousands of years. "It's going to take a while for that area to not be over the hot spot."

In the long geologic perspective, Kilauea's lava flows "are happening pretty quickly," said Mertzman, even though there may be 10, 15, or 30-year intervals between significant lava eruptions.

And during the periods when Kilauea stops erupting lava, that seems to be when Mauna Loa comes alive again. The large mountain may be ancient, but it's not nearly done.

"If one is erupting, the other isn’t," said Phoenix.

Mertzman said it's likely Mauna Loa will awaken sooner rather than later.

"One of these days you’ll be writing about the eruptions on the summit of Mauna Loa," he said. "It’ll surely happen in your lifetime."

Lava flows on Mauna Loa, both historic and ancient.

Image: usgs

And there's a good chance islanders will have to move out of the path of this creeping lava. According to the USGS, 90 percent of Mauna Loa's sprawling surface is covered in geologically young lava flows that have occurred in the last 4,000 years.

Locals living on or near these volcanoes are well-aware of the risks here, and the continuing story of lava flows, close calls, and engulfed homes, said Phoenix. This is especially the case for gushing Kilauea, which is acting just as it should if it ever wants to grow into something approximating its looming predecessor, Mauna Loa.

"That's why you don’t make your house out of the finest Italian marble," said Phoenix.

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